Reported in the December 11 issue of Science, an analysis of Tawa hallae, a meat-eating theropod dinosaur between two-and-four meters long, reveals that the early history of theropods was characterized by waves of migration from South America, not just localized or regional species diversification.
“To understand how these early theropods were related evolutionarily, we analyzed hundreds of morphological features then used recently devised statistical methods to model how the distributions of these dinosaurs evolved during the Triassic,” says Alan H. Turner, Ph.D., Assistant Professor of Anatomical Sciences at Stony Brook University and a co-author of the study.
Originally excavated in 2006 at Ghost Ranch in northern New Mexico, two nearly complete skeletons and several other partial specimens of Tawa hallae provided the scientists with the samples they needed to complete a full anatomical analysis and model its evolutionary history. This anatomical information gathered from Tawa helped fit all Triassic theropod dinosaurs into the evolutionary tree of the group.
At Ghost Ranch, Dr. Turner and colleagues observed three distantly related carnivores in the Late Triassic beds, which implied that each carnivore descended from a separate lineage before arriving in North America, instead of all three evolving from one local ancestor. The skeletons of Tawa found in that area display characteristics that exist in the two others excavated at Ghost Ranch, fossils from a carnivore closely related to Herrerasaurus, which lived in South America, and Coelophysis, common to North America. Yet, Tawa also had features of neither, which indicates a separate lineage.
Tawa is an example of a fossil that fills a morphological gap, which arises when a fossil record is incomplete. The researchers point out that the fossil is not a missing link on the dinosaur evolutionary chain, as it evolved on its own lineage. In addition, because Tawa was well preserved and a complete skeleton, the team was able to answer a lot of questions that normally surface when examining fossil lineage.
“One of the biggest morphological gaps in early dinosaurs lies between Herrerasaurus and animals that are clearly more related to birds, such as Coelophysis or Dilophosaurus,” explains Sterling Nesbitt of the University of Texas at Austin, the lead author of the study. “Tawa fits perfectly in between, morphologically. It retains characteristics that existed in Herrerasaurus that we thought were more primitive while also possessing features seen in unmistakable theropods (including birds), such as the presense of air sacs surrounding the braincase and neck.”
Dr. Turner, an expert on theropod dinosaur evolution and biogeography, the study of how and where organisms distribute around the world, explains that in the Triassic when Tawa and animals like them were evolving all the continents were united in a single landmass called Pangaea. However, by the Late Triassic North America was becoming isolated from present day continents (i.e., South America, Europe). Isolation is an important aspect of the speciation process, and thus evolution.
“Based on this, we had predicted that the theropod dinosaurs we were finding in North America at Ghost Ranch would form their own group, or clade, separate from their South American cousins. What we found from the data was the opposite,” says Turner.
“The North American dinosaurs did not form an endemic group. We discovered that their closest relatives lived in South America, not North America. This indicates that long range dispersal was prevalent at the time.”
Dr. Turner says that the team’s anatomical analysis, combined with biogeographic tests detailed in the study demonstrate that Triassic carnivorous dinosaurs from the quarry dispersed multiple times into North America. Dispersal of early dinosaurs it seems was prevalent during the Triassic, suggesting that the lack of sauropodomorph (long-necked) dinosaurs in North American was not a result of physical barriers.
“We don’t know why sauropodomorphs were not in North America, but it looks increasingly likely that they were getting here but something was preventing them from staying,” says Turner.
“Many questions remain but discoveries like Tawa are allowing us to evaluate these questions in ways we were not able to in the past.”
In addition to Turner and Nesbitt, authors include Nathan Smith of the University of Chicago and the Field Museum of Natural History; Randall Irmis of the Utah Museum of Natural History and the University of Utah; Alex Downs of the Ruth Hall Museum of Paleontology in New Mexico, and Mark Norell of the American Museum of Natural History.
The research for the study was supported by the National Science Foundation (NSF) through grants to individual researchers, as well as the National Geographic Society, the University of Chicago, the Field Museum of Natural History, the University of Utah, the Ruth Hall Museum of Paleontology, and Stony Brook University. To read more about Tawa, visit http://www.nsf.gov/news/special_reports/tawa/.
The Department of Anatomical Sciences is one of 25 departments within Stony Brook University School of Medicine. Fields of study include research on human evolutionary anatomy, morphology and vertebrate paleontology.
Greg Filiano | Newswise Science News
A promising target in the quest for a 1-million-year-old Antarctic ice core
24.05.2018 | University of Washington
Tropical Peat Swamps: Restoration of Endangered Carbon Reservoirs
24.05.2018 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences